1. Field of the Invention
The invention relates to a hybrid vehicle that has an internal combustion engine including in-cylinder injection valves and port injection valves, and an electric motor, as driving sources (power sources), and runs while controlling output torque of the driving sources.
2. Description of Related Art
A hybrid vehicle is equipped with an internal combustion engine and an electric motor, as driving sources that generate driving force for running the vehicle. Namely, the hybrid vehicle runs with torque generated by at least one of the engine and the electric motor and transmitted to a drive shaft connected to driving wheels of the vehicle.
In some cases, the hybrid vehicle is equipped with an internal combustion engine including a fuel injection valve (in-cylinder injection valve) that directly injects fuel into a combustion chamber of each cylinder, and a fuel injection valve (port injection valve) that injects fuel into an intake port that communicates with the combustion chamber. One type of the hybrid vehicle equipped with the engine including the in-cylinder injection valve and the port injection valve for each cylinder is adapted to run in a selected one of a port injection drive mode, an in-cylinder injection drive mode, and a both-injector drive mode, in order to make various diagnoses of malfunctions (see, for example, Japanese Patent Application Publication No. 2005-226553 (JP 2005-226553 A)). In the port injection drive mode, the total amount of fuel supplied to the engine is injected from the port injection valve. In the in-cylinder injection mode, the total amount of fuel supplied to the engine is injected from the in-cylinder injection valve. In the both-injector drive mode, fuel is injected from both the in-cylinder injection valve and the port injection valve.
One type of the hybrid vehicle in the related art has a system that determines power required to be generated by the engine (required engine power), based on torque determined according to the amount of accelerator operation by the user (user-requested torque required to be applied to the drive shaft of the vehicle). Furthermore, the system of the hybrid vehicle of the related art controls the engine so that the engine generates power that satisfies the required engine power, while assuring the optimum operating efficiency. In this case, the system controls the electric motor so that the motor generates output torque that makes up for a shortage of output torque of the engine transmitted to the drive shaft, relative to the user-requested torque.
When the user-requested torque is small (accordingly, the required engine power is small), and therefore, the engine is not able to operate at an efficiency equal to or higher than a given efficiency (when an engine operation stop condition is satisfied), the system of the hybrid vehicle of the related art stops operation of the engine, so that the user-requested torque is satisfied or provided solely by output torque of the electric motor. When the user-requested torque increases (accordingly, the required engine power increases) in a condition where the operation of the engine is stopped, and therefore, the engine becomes able to operate at an efficiency equal to or higher than the given efficiency (when an engine start condition is satisfied), the system of the known hybrid vehicle starts the engine, so that the user-requested torque is satisfied or provided by output torque of the engine and output torque of the motor. Thus, since the engine is stopped and started in this manner, or intermittently operated, the above operation of the engine is also called “intermittent operation” or “engine intermittent operation”.
In the engine as described above, it is desirable to make a determination (in-cylinder injection valve abnormality determination) as to whether an abnormality occurs to the in-cylinder injection valve, and make a determination (port injection valve abnormality determination) as to whether an abnormality occurs to the port injection valve. The engine needs to be operated in the above-mentioned in-cylinder injection drive mode in order to make an in-cylinder injection valve abnormality determination. Also, the engine needs to be operated in the above-mentioned port injection drive mode in order to make a port injection valve abnormality determination.
However, if the engine is kept operating in the port injection drive mode in a condition where the load of the engine is relatively high, the temperature in the vicinity of a fuel injection hole (nozzle) of the in-cylinder injection valve becomes excessively high. Accordingly, it is difficult to make a port injection valve abnormality determination when the engine is in a high-load condition.
In a condition where the load of the engine is relatively low, on the other hand, the engine can be kept operating in the port injection drive mode or the in-cylinder injection drive mode, over a relatively long period of time though there is a limit to the period. Accordingly, it is preferable to make an in-cylinder injection valve abnormality determination and a port injection valve abnormality determination (these abnormality determinations will be collectively called “injection valve abnormality determinations”), in a condition where the load of the engine is relatively low.
However, in the hybrid vehicle as described above, the required engine power is small when the load of the engine is small; therefore, the engine cannot be operated at an efficiency that is equal to or higher than the given efficiency, and the operation of the engine is stopped under the intermittent operation. Consequently, chances of making injection valve abnormality determinations are considerably reduced.
It is thus proposed to inhibit the operation of the engine from being stopped under the engine intermittent operation when any injection valve abnormality determination has not been made. However, if the operation of the engine is inhibited from being stopped so as to make an injection valve abnormality determination, the fuel efficiency of the engine (accordingly, the fuel efficiency of the hybrid vehicle) deteriorates.
In the meantime, when a catalyst warm-up request for increasing the temperature of a catalyst provided in an exhaust passage of the engine, a heating request for increasing the temperature within a compartment or cabin of the hybrid vehicle, or the like, is generated, the operation of the engine is inhibited from being stopped under the engine intermittent operation. Namely, in the hybrid vehicle, the operation of the engine may be inhibited from being stopped under the engine intermittent operation, for a purpose different from the purpose of making an injection valve abnormality determination. In the following description, a condition under which the operation of the engine is inhibited from being stopped under the engine intermittent operation, for a purpose different from the purpose of making an injection valve abnormality determination, will be called “general intermittent-operation inhibiting condition”. If an injection valve abnormality determination can be made during a period in which the general intermittent-operation inhibiting condition is satisfied, deterioration of the fuel efficiency may be reduced.
However, the frequency at which any general intermittent-operation inhibiting condition is satisfied is not so high. Furthermore, even if the general intermittent-operation inhibiting condition is satisfied, an injection valve abnormality determination cannot be made for the reason as described above if the engine is in an operation condition in which the load is relatively large, for example. Consequently, a problem of a delay in making an injection valve abnormality determination may arise again.